This invention pertains to mixed aliphatic/aromatic polycarbodiimides and more particularly to a method for their preparation.
The use of polycarbodiimides as the crosslinker for well-known carboxylated latexes has been demonstrated to provide a requisite combination of control as well as rapid reaction. In the search for polycarbodiimides useful as crosslinking agents, it was found that aliphatic polycarbodiimides were very useful. Unfortunately, the raw materials used to prepare the aliphatic materials are quite expensive. In an attempt to prepare lower cost polycarbodiimides, it was found that the aromatic isocyanates used to prepare aromatic polycarbodiimides were considerably less expensive. However, aromatic polycarbodiimides failed to yield acceptable rates and degree of crosslinking. Thus, it was felt that a co-polycarbodiimide containing the combination of both aliphatic and aromatic constituents formed by a proper mixture of aliphatic and aromatic isocyanates would yield the requisite crosslinking rate and acceptable cost parameters.
In the attempts to prepare the aliphatic/aromatic co-polycarbodiimide, it was found that these materials were much more difficult to prepare than either the fully aromatic or the fully aliphatic system. Using a procedure which satisfactorily yielded either of the all aliphatic or all aromatic polycarbodiimides, the mixed system often yielded gelled or extremely viscous materials having severe discoloration.
It is therefore an object of this invention to provide a method for preparing mixed aliphatic/aromatic polycarbodiimides in satisfactory yields.
Other objects will become apparent to those skilled in the art upon a further reading of the specification.